1. Field of the Invention
The present invention relates to orthopaedic implants, and, more particularly, to orthopaedic implants having a porous metal pad attached thereto.
2. Description of the Related Art
Orthopaedic implants, such as knee or hip implants, may include one or more porous surfaces at the exterior thereof. The porous surfaces enhance implant fixation within the bone by allowing bony ingrowth therein or penetration of bone cement. The porous surface is typically in the form of a pad constructed of fiber metal, metal beads or a wire mesh. The fibers, beads or wires are typically interconnected with each other using a sintering or diffusion bonding process. The porous metal pad is cut to shape to fit a supporting surface formed on the orthopaedic implant body.
One known method of attaching the porous metal pad to the implant body is to clamp the porous metal pad against the supporting surface of the implant body, and thereafter metallurgically bond the porous metal pad to the implant body using a diffusion bonding or sintering process. A problem with sintering the porous metal pad to the implant body is that this process is both time consuming and expensive from a manufacturing standpoint. For example, during sintering, the ramp up and cool down time for a sintering furnace is approximately 14 hours per cycle. If the porous metal pad is being connected, e.g., to the interior bone engaging surface of a femoral knee component, it may take a minimum of three cycles to complete the sintering operation. The complex geometric interior design of the femoral knee component may require that only one or two porous metal pads be attached to the femoral knee component during one cycle of the sintering process. The typical interior of the femoral knee component defines five distinct surfaces which require connection with a porous metal pad. Therefore, to completely bond the porous metal pad to the interior of the femoral knee component may require in excess of 42 hours of furnace time. Added to this is the time required to connect the clamping tool to the implant for holding the porous metal pad in contact with the supporting surface of the implant. It is thus apparent that providing a porous metal pad on an implant using a sintering process is relatively time consuming and expensive.
It is also known to diffusion bond a fiber metal pad to a thin metal foil, which in turn is attached to an orthopaedic implant body using a laser welding process. For details of such an attachment process, reference is hereby made to U.S. patent application Ser. No. 08/609,210, entitled "ORTHOPAEDIC IMPLANT AND METHOD OF MAKING SAME," which is assigned to the assignee of the present invention and incorporated herein by reference. In general, a porous metal pad, such as a fiber metal pad, is diffusion bonded to a thin metal foil. The fiber metal pad and thin metal foil are each configured to be received within a recess formed in the orthopaedic implant body. The edges of the thin metal foil extend to the exterior of the recess formed in the orthopaedic implant body. A laser welder is used to weld the thin metal foil to the orthopaedic implant body, and thereby indirectly attach the fiber metal pad to the implant body.
What is needed in the art is a method of attaching a porous metal pad to an orthopaedic implant body wherein the porous metal pad is attached to the implant body at locations other than the periphery of the porous metal pad.
What is further needed in the art is a method of attaching a porous metal pad to an implant body which is faster than a sintering process.